Unit 4 week 2 Flashcards
Presentation of adrenal insufficiency (BOTH primary and secondary adrenal insufficiency)
1) Hyponatremia
2) Hypotension
3) Hypovolemia
4) Tachycardia
5) Hypoglycemia
6) Eosinophilia
+ fatigue, weakness, postural dizziness, anorexia, nausea, vomiting, diarrhea, abdominal pain, weight loss, myalgias, arthralgias, headache
Presentation of adrenal insufficiency ONLY present with primary AI
1) Hyperkalemia
2) Hyperpigmentation
3) Salt craving
Adrenal Crisis
symptoms (6) and treatment
EMERGENCY
-nausea, vomiting, fever, syncope, hypotension, tachycardia
GIVE STRESS DOSE STEROIDS (Hydrocortisone 100 mg IV every 8 hrs)
Tests for diagnosis of adrenal insufficiency (4)
1) Cortisol level (7-8am cortisol not > 16-18 → check ACTH with cortrosyn)
2) Cortrosyn (synthetic ACTH): stimulation test of adrenal reserve
- Baseline serum cortisol + IV injection of ACTH → serum cortisol at 30 and 60 minutes
3) Adrenal CT scan
4) Serum ACTH level
Primary vs. Secondary Adrenal Insufficiency
Primary = adrenal gland is not producing cortisol
Secondary = any cause upstream of adrenals
- ACTH NOT being produced
- adrenals are normal and respond normally to AGII –> normal aldo levels
Causes of Primary adrenal insufficiency
1) Addison’s Disease (autoimmune destruction)
2) Infectious - TB (most common cause in developing countries), Fungi, HIV
3) Amyloid infiltration of adrenals
4) Hemorrhagic, Metastatic, Surgical destruction of adrenals
Presentation of Primary adrenal insufficiency (4)
1) Hyponatremia
2) Hyperkalemia
3) Hypotension
4) Hyperpigmentation
Why do patients with primary AI have hyperkalemia? Why do they have hyperpigmentation?
Hyperkalemia due to lack cortisol AND ALDOSTERONE → hyponatremia, hyperkalemia
Hyperpigmentation due to Increased POMC (large ACTH precursor molecule)
–> increased ACTH and MSH (melanocyte stimulating hormone)
Diagnosis of Primary AI
4 tests and their findings
1) *Serum cortisol < 5ug/dL at baseline
2) *Plasma ACTH > 100 pg/ml
3) *Serum cortisol < 20ug/dl after Cosyntropin (ACTH stim test)
4) Adrenal CT Scan:
Small glands → autoimmune, metabolic
Large glands → all other causes
Treatment of primary adrenal insufficiency
glucocorticoids and mineralocorticoid replacement
- Hydrocortisone or prednisone (GC)
- Fludrocortisone (MC)
Causes of secondary adrenal insufficiency (3)
1) Supraphysiological exogenous glucocorticoids for > 3 weeks
2) Opioids
3) Hypothalamic/pituitary lesions (tumor, surgery, radiation, infection, hemorrhage, infiltrative, metastatic)
Presentation of secondary adrenal insufficiency
1) Hyponatremia
2) Hypotension, hypovolemia
3) NORMOkalemic (preserved aldo synthesis)
4) Low ACTH
5) No hyperpigmentation
Diagnosis of secondary adrenal insufficiency (4)
tests + results
1) Serum cortisol < 5ug/dl baseline
2) Serum cortisol < 20ug/dl after Cosyntropin (chronic secondary AI - may have normal ACTH response if this is new onset of AI and adrenals haven’t atrophied)
3) Plasma ACTH low or normal
4) MRI pituitary may show pathology
Treatment of secondary adrenal insufficiency
replace GCs only
No MC replacement required
Adrenal medullary catecholamines synthesis
what is rate limiting step?
what step does cortisol effect?
Tyrosine → DOPA (via tyrosine hydroxylase = RATE LIMITING STEP)
DOPA → DA → NE
NE → epinephrine (via PNMT = UPREGULATED BY CORTISOL)
Pheochromocytoma
Tumor of dark chromaffin cells → excess NE and epinephrine
Paraganglioma
pheochromocytoma outside the adrenal medulla
Genetics of pheochromocytoma
commonly associated with genetic abnormalities and familial syndromes
MEN (2A, 2B) - Ret gene mutation
VHL
NF-1
SDHB
SDHD
SDHB vs. SDHD genes in pheochromocytoma
SDHB = gene that significantly increases risk for malignant pheochromocytoma
- Dopamine secreting tumor associated with malignancy
- B FOR BAD
SDHD = AD, paternal inheritance
D FOR DAD
RET gene and pheochromocytoma
mutated in MEN2A, 2B
RET cell surface receptor somatic mutation → constitutive activation
Glial-derived neurotrophic growth factor (GDNF) binds RET → intracellular signaling stimulating cell synthesis of NE and EPI
Constellation of findings in: MEN2A (3)
Pheochromocytoma
Medullary thyroid carcinoma (Calcitonin-secreting C cells)
Hyperparathyroidism
Constellation of findings in: MEN2B (3)
Pheochromocycoma
Medullary thyroid carcinoma
Mucosal neuromas
Constellation of findings in: VHL (6)
pheochromocytoma RCC renal/pancreatic cysts CNS hemangioblastomas islet cell tumors retinal angiomas
Constellation of findings in: NF-1 (5)
pheochromocytoma hyperparathyroidism duodenal carcinoids medullary thyroid carcinoma optic nerve tumors
Clinical manifestations of pheochromocytoma
triad of symptoms + 3 other findings
TRIAD = headache, palpitations, diaphoresis
Hypertension (a1 vasoconstriction)
-Severely resistant to treatment
Increased HR, sweating and tremulousness (B1 receptors increase inotropic and chronotropic heart effects)
Vasodilation in muscle beds (B2 receptors)
Diagnosis of pheochromocytoma (3 tests)
1) 24 hour urinary collection
2) CT/MRI to localize tumor
3) I-123 MIBG scan: localization for extra-adrenal, recurrent, and metastatic tumors
24 hour urine collection in pheochromocytoma
- Catecholamines (Epi, NE) –> Not as reliable, needle stick can cause a rush of catecholamines
- Metabolites (metanephrines, normetanephrines, VMA) (can do serum also)
Medications that can interfere with 24 hr urine levels of catecholamines and metabolites (4)
Interfering medications: can falsely elevate catecholamines / metabolites
Acetaminophen
SSRIs, SNRIs
Marijuana and other illicit drugs
Treatment of pheochromocytoma
1) Surgical removal
2) Alpha-adrenergic blocker (phenoxybenzamine)
3) B-blocker (labetalol)
DO NOT start B-blocker before a-blocker
4) Ca2+ channel blocker
Licorice ingestion and hyperaldosteronism?
(pseudohypoaldosteronism): licorice prevents inactivation of cortisol in kidney
→ HTN and hypokalemia
Causes of secondary aldosteronism (2)
Cirrhosis
Heart failure
Primary aldosteronism (Conn’s Syndrome)
Adrenal cortex (glomerulosa) primarily secretes too much aldosterone
- Low renin and angiotensin II (under normal feedback mechanisms)
- RAAS feedback loop is perturbed
Most common cause of secondary hypertension
Primary aldosteronism (Conn’s Syndrome)
Presentation (6)
1) Resistant hypertension
- HTN at a young age, HTN resistant to multiple anti HTN meds, stage 2 HTN (>160/100)
2) Hypokalemia - may be very severe or normal
3) Metabolic alkalosis
4) Muscle weakness
5) Mild hypernatremia
6) Presence of adrenal adenoma possible
Primary aldosteronism (Conn’s Syndrome)
Diagnosis (4)
1) Aldosterone:Renin Ratio: ratio > 20
- High plasma aldosterone, low plasma renin
2) IV saline suppression test
-IV saline should suppress aldosterone, but if they have primary aldosteronism → no aldo suppression
Aldo > 10 ng/dL confirms dx
3) CT or MRI to look for adenoma or hyperplasia
4) Adrenal Vein Sampling (AVS) for lateralization (look for difference in aldosterone levels between R and L adrenal vein)
Which medications should be stopped before getting plasma renin and aldosterone levels?
Must STOP interfering medications before testing (spironolactone, eplerenone)
Treatment of primary aldosteronism
Surgical cure
Bilateral adrenal hyperplasia or non-surgical candidate → treat with mineralocorticoid antagonist (spironolactone or eplerenone)
4 types of primary aldosteronism
1) Aldosterone producing adenoma (34%)
2) Idiopathic hyperaldosteronism (bilateral adrenal hyperplasia) (66%)
3) Glucocorticoid remediable hyperaldosteronism
4) Aldosterone-producing carcinoma
Glucocorticoid remediable hyperaldosteronism
mechanism?
genetic rearrangement fusing regulatory promoter of 11-B hydroxylase with structural component of aldosterone synthase → aldosterone synthase under positive control of ACTH
–> increased aldosterone synthesis in response to ACTH
3 main categories of Cushing’s Syndrome
1) Iatrogenic (chronic administration of GCs - most common)
2) ACTH dependent
3) ACTH independent: high cortisol production, low ACTH, feedback mechanism still works
Causes of ACTH dependent Cushing’s Syndrome
1) Pituitary adenoma (Cushing’s Disease)
2) Ectopic ACTH Syndrome (small cell lung cancer)
Pituitary adenoma (Cushing’s Disease)
ACTH and cortisol levels
High ACTH, high cortisol
Feedback mechanism does not turn off ACTH
Ectopic ACTH Syndrome
ACTH and cortisol levels
VERY high ACTH, VERY high cortisol
Feedback mechanism does not turn off ACTH
Causes of ACTH independent Cushing’s Syndrome
Adrenal Adenoma
Adrenal Carcinoma
Nodular Adrenal Hyperplasia
high cortisol production, low ACTH, feedback mechanism still works
3 steps for working up Cushing’s syndrome
1) Establish patient has Cushing’s syndrome
2) Determine etiology of hypercortisolism ACTH level (ACTH dependent vs. independent)
3) 3) Determine if ACTH is ectopic or from pituitary
Tests that can establish if a patient has Cushing’s syndrome (3)
1) 24 hr urinary free cortisol
2) 1 mg dexamethasone suppression test (cortisol should be low after dexamethasone)
3) Midnight salivary cortisol elevated (cortisol should be LOWEST at midnight)
What test can distinguish between ACTH dependent vs. independent Cushing’s Sydrome
ACTH level
How can you determine if ACTH production is ectopic or from pituitary? (3 tests)
1) CT, MRI, ultrasonography, isotope scanning
2) 8 mg dex suppression test
3) Inferior petrosal sinus sampling
8 mg dex suppression test - for what? tells you what?
determine if ACTH production is ectopic or from pituitary
Pituitary source: cortisol suppresses to < 5 ng/dL because still some sensitivity of pituitary corticotroph cells
Not very reliable
Inferior petrosal sinus sampling
measure baseline ACTH at intervals after stimulation with CRH
Pit source → ACTH should be higher in petrosal sinus than central IVC
Ectopic source → ACTH similar in sinus and central IVC
Adrenal incidentalomas
adrenal gland tumors are common, most clinically insignificant, majority are non-functioning
Initial evaluation of Adrenal incidentalomas must exclude:
1) Benign or Malignant? Radiographic appearance
2) Functional or nonfunctional?
Determining benign or malignant nature of adrenal incidentaloma
Malignant: size? shape? lipid density? signal intensity?
Benign: < \_\_\_\_\_\_\_ size \_\_\_\_\_\_\_ with \_\_\_\_\_\_\_\_ borders HU is \_\_\_\_\_\_ on noncontrast CT \_\_\_\_\_\_\_ lipid content \_\_\_\_\_\_\_\_\_\_ occurs on out of phase imaging
Malignant: Large, irregular, lipid-poor lesion with higher signal intensity (high HU, > 10)
Benign:
-< 4 cm in size
-Homogenous with smooth/regular borders
-HU < 10 on non-contrast CT
-High intracellular lipid content, density closer to water and fat
-Signal dropout on out of phase imaging
Rapid enhancement of contrast, rapid loss of contrast (>50% washout)
MRI is as effective as CT scanning for distinguishing benign from malignant lesions
Adrenal incidentalomas
Functional or nonfunctional?
what tests should you order to determine this? (3)
1) Plasma metanephrines or 24 hr urine mets/cats
SCREEN FOR PHEOCHROMOCYTOMA
2) 1 mg overnight dex suppression test
SCREEN FOR HYPERCORTISOLISM
3) If patient is hypertensive, screen for primary aldosteronism with aldosterone/plasma renin level
Adrenocorticosteroids:
____________ effects can NOT be separated from anti-inflammatory effects and ___________ effects cannot be separated from immunosuppressive effects
Metabolic effects can NOT be separated from anti-inflammatory effects and anti-inflammatory effects can NOT be separated from immunosuppressive effects
Hydrocortisone
MC:GC Activity
Route of administration
Clinical Use
MC:GC Activity: 1:1
Route of administration: TOPICAL, oral, injectable
Clinical Use:
- Used in PHYSIOLOGIC replacement regimens
- Must be given several times daily
Prednisone
MC:GC Activity
Route of administration
Clinical Use
MC:GC Activity: 1:5
Route of administration: oral (NOT TOPICAL)
Clinical Use: most commonly used oral agent for steroid burst therapy
Dosing considerations with prednisone?
MUST be activated to prednisolone in liver**
Cannot be given topically
Dexamethasone
MC:GC Activity
Route of administration
Clinical Use
Adverse effects
MC:GC Activity: 0:30 → all GCC activity
Route of administration: oral, injectable, TOPICAL
Clinical Use: used for anti-inflammatory/immunosuppressive actions
- Most potent anti-inflammatory agent
- Used in cerebral edema, chemo-induced vomiting
- Big suppression of ACTH secretion from pituitary
Adverse effects: Significant metabolic side effects
Triamcinolone
potent systemic agent with excellent topical activity
NO MC action
Fludrocortisone
MC:GC Activity: 125-200:10 → Primarily MC activity without GC / anti-inflammatory activity
High doses can cause hypokalemia
Treatment of Addison’s Disease
reat with physiologic replacement therapy (MC and GC replacement required)
Cortisol (GC replacement) + Fludrocortisone (MC replacement) + DHEA (sex steroid replacement for women)
3 main categories of drugs that can be used to treat Cushing’s Syndrome
1) ACTH secretion inhibitors
2) Cortisol synthesis inhibitors
3) Cortisol Receptor Antagonist
ACTH secretion inhibitors (2)
Cabergoline (D2 agonist)
Pasireotide (SST analog)
Ketoconazole
Cortisol synthesis inhibitor
inhibits CYP450 androgen synthesis in testes and inhibits cholesterol → pregnenolone, reduces cortisol synthesis
Adverse effects: headache, N/V, gynecomastia, impotence, reversible hepatotoxicity
Mifepristone
Cortisol Receptor Antagonist
-anti-progestational drug that blocks GC receptors at higher doses
Not first line
Used to control hyperglycemia secondary to hypercortisolism
Contraindicated in pregnancy
Treatment of Primary aldosteronism
goal is to normalized hypokalemia and BP before surgical removal of tumor
Aldo antagonists: Spironolactone, eplerenone
BP meds: Ca2+ channel blockers, ACEI, ARB
Metyrosine
competitive inhibitor of catecholamine synthesis
used to treat pheochromocytoma that is non-surgical
Thyronine
backbone of THs with 3, 5, 3’, and 5’ positions that can be iodinated
Thyroxine (T4) vs. T3
Thyroxine (T4) = 3, 5, 3’, 5’ tetraiodothyronine
T3 = 3, 5, 3’ triiodothyronine
Iodide trap
Membrane pump on basal side of follicular cell promotes accumulation of iodide in thyroid 30-40x concentration in serum
4 steps of iodine uptake by thyroid gland
1) Na+/I- symporter + Na/K ATPase on basal side brings I- into cell
2) Iodide diffuses from basal (blood) → apical (lumen) side of follicular cell
3) Iodide oxidized (I- → I2) by thyroid peroxidase
4) Organification of I2 (incorporation of iodide into tyrosyl residues on thyroglobulin) occurs at follicular cell-colloid interface
Thyroperoxidase
membrane bound glycoprotein/enzyme in thyroid that catalyzed iodination of thyroglobulin, organification of I2, and coupling of DITs/MITs
Synthesis and Release of Thyroglobulin
Thyroglobulin synthesized in RER of follicular cell and transported to Golgi apparatus to be glycosylated and packaged into secretory vesicles
Secretory vesicles released from apical follicular cell into lumen (colloid)
Undergoes iodination and coupling reactions to synthesize TH at tyrosyl residues
Steps of Thyroid Hormone Synthesis
thyroperoxidase catalyzes iodination of tyrosyl moieties on TG → mono/di- iodotyrosine (MIT/DIT) formed on TG
Thyroperoxidase also catalyzes coupling of 2 DITs or 1 DIT and 1 MIT to form iodothyronines
Steps of thyroid hormone release
Drops of colloid endocytosed into follicular cells → coalesce with lysosomes → lysosomal enzymes act on TG to cleave T4 and T3 from TG
10-20x more T4 removed than T3
Thyroid Hormone Transport
Most thyroid hormone in a protein bound form
Some exist in free form (0.03% of T4, and 0.4% of T3)
thyroid hormone in a protein bound form
binds with what 3 proteins?
what is the effect of protein binding?
Thyroid binding proteins:
1) Thyroid binding globulin (TBG)
2) Thyroid binding pre-albumin (TBPA)
3) Albumin
Delay, buffer and prolong effects of TH action
half life of T4 vs. T3
T ½ for T4 is 7 days, and T3 is 1 day because TBG has a higher affinity for T4
Free thyroid hormone
Free form is active form
Must measure plasma TH values for bound or free form in addition to total TH in blood
How is T4 converted to T3?
T4 → T3 by 5’-deiodinase in the target cell
Cellular actions of thyroid hormone
- T3 has a higher affinity for TH receptor, so is more active than T4
- T3/T4 enter cell by ACTIVE TRANSPORT
T4 → T3 by 5’-deiodinase
T3 enters nucleus → interacts with nuclear receptors → T3-receptor complex acts on DNA to direct transcription of specific mRNAs
5 main actions of thyroid hormone
1) Metabolic rate
2) Fetal and neonatal brain development
3) TH and GH necessary for normal growth
4) Enhance response to catecholamines
5) Metabolic effects
How does thyroid hormone effect metabolic rate?
THs increase basal metabolic rate and increase oxygen consumption = Calorigenic effect
Mostly due to Na/K pump upregulation
Thyroid hormone and catecholamines
TH enhances response to catecholamines: TH mimics effects of SNS by increasing number of B-adrenergic receptors = permissive effect
Thyroid hormone and metabolic effects
low/moderate dose of TH vs. high dose of TH
Low/Moderate doses of TH → anabolic
-Promote conversion of glucose → glycogen
High doses of TH → catabolic
-Increased fuel consumption, protein breakdown, muscle wasting, glycogenolysis, and lipolysis
TSH and its actions on the thyroid gland
TSH → thyroid gland where it interacts with membrane receptor, stimulating thyroid hormone synthesis via increases in cAMP
TSH stimulates:
1) Iodide pump
2) Thyroperoxidase
3) Endocytosis of colloid
4) Iodide organification
5) Coupling of iodotyrosines
6) TG synthesis and its proteolysis following endocytosis
7) Follicular cell proliferation, elongation, and enlargement
3 drugs that block thyroperoxidase and conversion of T4 to T3 in target cells
Thioureas, propylthiouracil, methimazole
Signs/Symptoms of Hyperthyroidism (10)
BMR Nervousness Pretibial myxedema (Graves) Heat intolerance Muscle weakness Goiter Palpitations Exophthalmos (Graves) Lid retraction (Graves) Tachycardia
In what cases would you have an elevated total T4/T3, but a normal free T4/T3?
Total T4/T3 can be elevated with increases in thyroid binding proteins (e.g. high estrogen states), but free T4/T3 will not be affected
4 causes of high uptake aka “TRUE” Hyperthyroidism
Graves Disease (autoimmune thyrotropin receptor antibody)
Toxic adenoma
Toxic multinodular goiter
Tumors of pituitary or thyroid
What is low uptake “hyperthyroidism”?
release of preformed T3/T4 into blood (NOT TRUE HYPERTHYROIDISM) → thyroid scan will be dark, no need for scan
Causes of low uptake “hyperthyroidism” (7)
1) Granulomatous thyroiditis (viral) = de Quervain’s → tender thyroid
2) Chronic lymphocytic thyroiditis (Hashimoto’s)
3) Postpartum thyroiditis
4) Radiation, infectious thyroiditis → tender thyroid
5) Drug-induced thyroiditis
6) Excess TH administration (Factitious)
7) Struma ovarii (ovarian tumor that produces thyroid hormones)
Grave’s Disease
symptoms?
antibodies against TSH receptor → stimulate excess T4/T3 production
Symptoms:
-Ophthalmopathy (thyroid eye disease) and pretibial Myxedema
Why does pretibial myxedema and ophthalmopathy occur in Grave’s disease?
Occurs due to TSH receptor on fibroblasts → fibroblast overproduction of glycosaminoglycans (GAGs)
Tests that indicate Grave’s disease
Homogenous uptake, “hot scan” on radioactive iodine scan
Low TSH, high free T4 and T3
4 treatment options for Grave’s Disease
1) Antithyroid drugs (methimazole, propylthiouracil) → inhibit TH synthesis
2) Beta blockers → reduce systemic hyperadrenergic symptoms
3) Radioactive Iodine
4) Surgery
Thyroiditis
Types: subacute/granulomatous thyroiditis, postpartum thyroiditis
High release of preformed/stored T3/T4 as thyroid cells are damaged → high free T3, T4 and suppress TSH
Once destruction as resolved, there is no ability to secrete thyroid hormone → high TSH, low thyroid hormone = hypothyroid
NOT true hyperthyroidism (no overproduction of TH)
Signs/Symptoms of Hypothyroidism (10)
BMR Lethargy, weakness Myxedema Cold intolerance Slow speech Goiter Hoarseness Mental slowness Psychosis Bradycardia
Causes of Hypothyroidism (10)
1) Hashimoto’s Thyroiditis (chronic autoimmune)
2) Transient hypothyroidism
3) Iatrogenic: Thyroid surgery/thyroidectomy, Radioactive iodine, External neck irradiation
4) Iodine deficient diet or excess
5) Starvation, severe illness, severe stress, neonatal period (Euthyroid sick syndrome (nonthyroidal illness)
6) Liver or kidney disease (decreased serum protein binding)
7) Drugs (glucocorticoids, propranolol, amiodarone, radiocontrast dyes)
8) Infiltrative disease (TB, hemochromatosis, sarcoidosis, amyloidosis)
9) Cretinism
10) Pituitary tumor (central hypothyroidism)
why does Starvation, severe illness, severe stress, neonatal period cause hypothyroidism?
→ Inhibit conversion of T4 → T3 (active form) by blocking type 1 or type 2 deiodinase and activating type 3 deiodinase (converts T4 → rT3, inactive form)
Hashimoto’s Thyroiditis
Autoimmune destruction of thyroid gland
- most common cause of hypothyroidism in regions where iodine levels are adequate
- associated with HLA-DR5
Autoimmune destruction of follicular cells → initial dumping of thyroid hormone out of cells (hyperthyroidism) and progress to hypothyroidism
Cretinism
deficiency in neonates and infants
severe mental and growth retardation
short stature, skeletal abnormalities, coarse facial features, enlarged tongue, umbilical hernia
-can be caused by maternal hypothyroidism during early pregnancy, thyroid agenesis, dyshormonogenetic goiter, and iodine deficiency
__________ and __________ antibodies are often present in Hashimoto Thyroditis as a sign of thyroid damage
Antithyroglobulin
Antithyroid peroxidase antibodies
Histological presentation of Hashimoto’s thyroditis (2 main features
chronic inflammation with germinal centers and Hurthle cells (eosinophilic metaplasia of cells that line follicles)
Increased risk for _________ with Hashimotos thyroditis
B-cell (marginal zone) lymphoma
presents as an enlarging thyroid glans late in disease course
Subacute granulomatous (De Quervain) Thyroditis
Granulomatous thyroiditis that follows a viral infection
Presents as a tender thyroid** with transiet hyperthyroidism
Self-limited
*rare progression to hypothyroidism
Riedel fibrosing thyroiditis
chronic inflammation with extensive fibrosis of thyroid gland
- presents as hypothyroidism + “hard as wood”, non-tender thyroid gland
- fibrosis may extend to involve local structures
- mimics anaplastic carcinoma
- classicaly seen in young female patient
Myxedema Coma
Complication of chronic, severe hypothyroidism (typically Hashimoto)
true endocrine emergency - decrease CO, bradycardia, respiratory depression, edema, AMS, hypothermia, metabolic derangements
High mortality rate
3 main tests used to evaluate thyroid dysfunction
1) Thyroid Stimulating Hormone
2) Free T4 (not free T3)
3) Radioactive iodine uptake and scan
TSH testing:
Primary hypothyroidism vs. primary hyperthyroidism
when is TSH level unreliable?
best test to screen for thyroid dysfunction
Primary hypothyroidism → elevated TSH, low thyroid hormone
–> Lack of negative feedback by thyroid hormone
Primary hyperthyroidism → low TSH
–> Excessive negative feedback by thyroid hormone
CANNOT rely on TSH when pituitary gland is abnormal
When should you check a T4?
Check T4 if TSH is low
Radioactive iodine uptake and scan
Normal/elevated iodine uptake in setting of low TSH → ?
Low iodine uptake in setting of low TSH → ?
Normal/elevated iodine uptake in setting of low TSH → autonomous production of thyroid hormone = true hyperthyroid state
Low iodine uptake in setting of low TSH → thyroid hormone excess due to high release of preformed thyroid hormone → destructive / inflammatory etiology (e.g. early Hashimoto’s, thyroditis)
thyroid adenoma
Benign thyroid nodule
Typically solitary nodule
Must carefully evaluate capsule (with biopsy) - cannot be differentiated follicular adenoma from follicular carcinoma with FNA
Papillary Thyroid Carcinoma
- Most common type of thyroid carcinoma (80%)
- Associated with ionizing radiation in childhood
- Well-differentiated
- Lymphatic spread
- Excellent prognosis
Follicular Thyroid Carcinoma
- Malignant proliferation of follicles surrounded by fibrous capsule WITH INVASION THROUGH CAPSULE = hallmark
- -> can distinguish from follicular adenoma (via biopsy, NOT FNA)
-metastasizes HEMATOGENOUSLY
Anaplastic Thyroid Carcinoma
- Highly invasive undifferentiated malignant tumor of thyroid
- seen in elderly
- very aggressive, poor survival
- rapidly growing mass with necrosis and hemorrhage
Medullary Thyroid Carcinoma is a malignant proliferation of what cell type?
what will it stain with immunostain?
what can deposit in the tumor?
Malignant proliferation of parafollicular C cells (neuroendocrine cells that secrete calcitonin)
- can get amyloid deposition of calcitonin in tumor
- Immunostains: thyroglobulin -, calcitonin +, chromogranin +
Associated with MEN2
Papillary Thyroid Carcinoma
Histology - 3 main features
1) papillae lined by cells with clear “ORPHAN ANNIE EYE” nuclei
2) Nuclear grooves
3) Papillae often associated with psammoma bodies
Anatomic imaging modalities (3)
Detect or characterize palpable or incidentally found thyroid nodule on other modalities
1) Ultrasound
2) CT Neck
3) MRI
Ultrasound used for work up of thyroid disease how?
no radiation, real time, doppler capability
- Best modality to detect/characterize thyroid nodule
- Best modality to detect lymph node metastasis in post-op patient of thyroid cancer
Used for real time guidance for FNA
CT Neck used for work up of thyroid disease how?
Useful to define local extension of cancer in adjacent structures
Detect abnormal lymph nodes in areas not visualized by US
Distant metastasis
MRI used for work up of thyroid disease how?
Useful in identifying infiltrative disease particularly in post-therapy neck where anatomy is distorted
Detection of invasion of adjacent structures and deep nodal disease
NOT used to detect or characterize thyroid nodule
Iodine scanning can be used for what in working up thyroid dysfunction?
Functional imaging
Evaluate for function of thyroid gland or nodule in patient with abnormal thyroid function
Evaluate for distant metastatic disease
I-123 vs. I-131 iodine scans
I-123 scan: evaluate function of thyroid gland and thyroid nodule in patient with abnormal thyroid function (diagnostic only)
I-131 scan: diagnostic and therapeutic role
- Detect local/distant thyroid cancer metastasis
- Treatment of hyperthyroidism and well differentiated thyroid cancer
On a CT neck, the normal thyroid is _________ on noncontrast and _________ with IV contrast
Hyperdens on noncontrast
Hypervascular with IV contrast
Fetal thyroid gland arises from 2 distinct embryonic lineages
1) Follicular cells (endodermal pharynx) → produce thyroxine (thyroid hormone)
2) Parafollicular cells (neural crest) → produce calcitonin
After descent, thyroid follicular cells differentiate to express genes essential for ________________
thyroid hormone synthesis
Thyroid follicular cells trap iodide and secrete thyroid hormone by ________ wks.
Maternal ______ crosses the placenta for hormone synthesis
______ and ______ levels gradually increase to term
Trap iodide, secrete thyroid hormone, and TSH by 10-12 wks
Maternal iodine crosses placenta for hormone synthesis
TSH and T4 levels gradually increase to term
Hypothalamus-Pituitary-Thyroid axis is functional with feedback control by __________ wks
25 weeks
Thyroid gland originates as proliferation of _________ cells on median surface of __________ between ____ and ____ arches
Initially hollow → becomes solid and bilobed
Thyroid gland originates as proliferation of endodermal epithelial cells on median surface of pharyngeal floor between 1st and 2nd arches
Initially hollow → becomes solid and bilobed
Thyroid gland is connected to the ______ via the ________ as it descends. It completes this descent by the ______ week.
two problems that can arise due to thyroglossal duct problems?
Thyroid connected to TONGUE via THYROGLOSSAL DUCT as it descends
Completes descent in 7th gestational week
Can have arrested descent of thyroid or thyroid duct cyst
What if fetus doesn’t make thyroid hormone? How can fetus still get some thyroid hormone?
Placenta allows small amount of maternal T4 and iodine across → maternal T4 converted to T3 by type II deiodinase in fetal brain
→ minimizes adverse effects of fetal hypothyroidism
Transcription Factors Important for Thyroid Development (3)
1) PAX8
2) TITF1
3) TITF2
PAX8
paired box gene 8 transcription factor
Mutation causes thyroid dysgenesis
AD pattern of inheritance
Phenotypes vary from mild to severe hypoplasia (compensated or overt hypothyroidism)
Can be associated with renal agenesis
TITF1
Mutation can cause thyroid dysgenesis
Also expressed in lung, forebrain, and pituitary gland
Heterozygous mutation → CH, respiratory distress, neuro disorders
TITF2
thyroid transcription factor 2
Mutation can cause thyroid dysgenesis
Homozygous mutation → Bamforth Lazarus Syndrome
Bamforth Lazarus Syndrome
Congenital Hyothyroidism, cleft palate, spiky hair, bifid epiglottis, choanal atresia
Congenital hypothyroidism
lack of thyroid hormones present from birth
If not detected/treated early, can cause irreversible neurological problems and poor growth
Associated with other congenital abnormalities
4 causes of Congenital hypothyroidism
1) Thyroid Dysgenesis
2) Thyroid dyshormonogenesis
3) TSH resistance
4) Transient forms
5) Central Hypothyroidism
Thyroid Dysgenesis
- defect in what?
- causes ____% of congenital hypothyroidism
- due to _____, ______ or ______ (most common)
- female:male ratio?
-caused by defects in what transcription factors?
defect in thyroid gland development
85% of congenital hypothyroidism
Aplasia, hypoplasia, or **ectopy (most common - thyroid gland arrests in descent)
Female:Male 2:1
Caused by transcription factor defects (PAX8, TITF1, TITF2)
Thyroid dyshormonogenesis
- defect in what?
- causes ____% of congenital hypothyroidism
- can be caused by a mutation in what genes?
defect in thyroid hormone synthesis
10-15% of congenital hypothyroidism
Can be caused by mutations in genes coding for proteins involved in thyroid hormone synthesis
Most common is thyroid peroxidase gene mutation
AR inheritance
Goiter may be present
Pendred Syndrome
Type of thyroid dyshormonogenesis
AR mutation in SLC26A4 encoding pendrin protein that mediates iodide efflux from follicular cell to colloid
Goiter
Sensorineural congenital deafness (dilated semicircular canals on CT)
Thyroid phenotype mild and depends on nutritional iodine intake
Does not present in newborn period
TSH resistance
mutation in TSH-R transmembrane receptor on surface of follicular cells
Mediated effects of TSH
Critical for development and function of thyroid gland
TSH resistance:
- heterozygous loss of function mutation –> ?
- Homozygous TSH-R mutations →
Heterozygous loss of function mutations → partial resistance with normal size gland and TSH elevation
Homozygous TSH-R mutations → congenital hypothyroidism with hypoplastic gland and decreased T4 synthesis
Transient forms of congenital hypothyroidism (4)
1) Maternal TSH-R blocking abs
2) Maternal iodine deficiency or excess
3) Maternal radioiodine administration
4) Maternal medications (amiodarone, propylthiouracil, methimazole)
Central Hypothyroidism
(Hypothalamic/Pituitary Deficiencies)
Usually in setting of multiple pituitary hormone deficiency especially growth hormone deficiency
Must evaluate other pit. hormones and obtain cranial MRI
Treatment of congenital hypothyroidism
start treatment with levothyroxine AS EARLY AS POSSIBLE
Newborn screening for congenital hypothyroidism
Best to do after 2-3 days of age due to initial TSH surge after birth
1) Primary T4 screening (most common)
or
2) Primary TSH screening
Follow screening with confirmatory labs
Primary T4 screening in newborn screen
If T4 in lowest 10% of results on a given day → measure TSH
- If TSH > 20 = abnormal → call PCP
- If TSH < 20 could still be abnormal, but will not call PCP
Total T4 = bound + free
Can get inaccurate results in presence of extreme variations in concentrations of thyroid-binding proteins
Normal TSH secretion in first week of life:
Within 30 minutes of birth, TSH rapidly peaks to 60-80 uU/ml, then decreases → peak in T4 and T3 levels by 24 hours
T3-Uptake screening:
T3 uptake and T4 in SAME direction → ?
T3 uptake and T4 in OPPOSITE direction →?
used to differentiate central hypothyroidism and thyroid binding globulin deficiency
T3 uptake and T4 in SAME direction → thyroid disease
-Low uptake and low T4 = hypothyroid
T3 uptake and T4 in OPPOSITE direction → TBG abnormality
-High uptake and lw T4 → TBG deficient
Signs/Symptoms of Congenital Hypothyroidism (8)
**Baby appears normal at first - sx may not develop for weeks
Large posterior fontanel
Prolonged jaundice
Macroglossia
Umbilical hernia
Hypotonia
Feeding difficulties
Hoarse cry
Thyroid hormone reversibly bound in plasma to thyroid-binding-globulin (TBG), and only unbound hormone has metabolic activity
what drugs can increase TBG binding? (3)
what drugs can decrease TBG binding? (5)
- Increase binding with: estrogens, SERMs, Tamoxifen
- Decreased binding with: salicylates, anti seizure meds (phenytoin, carbamazepine), androgens, glucocorticoids, furosemide
T4 must be activated to T3, biologically active thyroid hormone, done by _________ in _______
T4 must be activated to T3, biologically active thyroid hormone, done by 5’-deiodinase in liver
drugs that can decrease activity of 5-deiodinase (4)
glucocorticoids, B-blockers, propylthiouracil, amiodarone
Levothyroxine (T4)
drug of choice for thyroid hormone replacement therapy
Use: hypothyroidism, myxedema coma (end state of untreated hypothyroidism)
Narrow therapeutic index
Takes 6-8 weeks of maintenance dose to reach steady-state plasma levels
Oral or IV, generic and cheap
Use same levothyroxine product throughout treatment for any individual patient
Levothyroxine (T4)
Adverse reactions (1) + caution starting this med in what patients?
symptoms of hyperthyroidism
Use caution initiating therapy if underlying cardiac disease
Bioavailability of Levothyroxine can be modified by impaired absorption caused by what drugs? (3)
Metal ions (antacids, calcium and iron supplements)
Ciprofloxacin
bile acid sequestrants
Liothyronine
(T3):
Well absorbed, rapid action, shorter duration
Allows for quicker dosage adjustments
NOT recommended for routine replacement (plasma level fluctuates)
Higher potential for cardiovascular side effects during initiation of therapy
More expensive
Liotrix
(T3, T4 mixture):
More expensive, no real advantage, not really used
Thyroid USP
porcine thyroid extract
Disadvantages: protein antigenicity, product instability, variable T4/T3 ratio may produce unexpected toxicity
Use in hypothyroidism NOT recommended
Thionamides
drug names?
Mechanism?
combine with what other med?
Methimazole, Propylthiouracil (PTU)
Mechanism: block iodine organification AND coupling of iodotyrosines → prevent T4/T3 synthesis
Pros: leaves gland intact
Combine with B-blocker (Propranolol blocks T4 → T3 conversion)
Methimazole
generally preferred over PTU
Efficacy at lower doses
Once-daily dosing
Fewer side effects
PTU preferred in __________
pregnancy
PTU and Methimazole
Side effects
Caution in pregnancy (can cross placenta) - PTU more protein bound so crosses less freely
Pruritic rash, GI intolerance, arthralgias
Agranulocytosis
Rare hepatotoxicity
Iodides (I-)
mechanism?
use?
disadvantages?
Mechanism: inhibit hormone synthesis and hormone release through inhibition of thyroglobulin proteolysis
Use: Rapid effects, used in thyrotoxicosis and thyroid storm
Disadvantages: variable effects, can worsen hyperthyroidism
Radioactive iodine (131I)
Mechanism?
Advantages?
Disadvantages?
Concentrated in thyroid → slow inflammatory process that destroys parenchyma of gland over weeks to months
Advantages: easy administration (oral), effective, inexpensive, no pain
Permanent resolution of hyperthyroidism
Disadvantages: slow onset of effects, radiation thyroiditis, may worsen ophthalmopathy, can cause hypothyroidism (80% require replacement therapy)
Treatment of Graves’ Disease:
1) ________ and _________ → modify tissue response, symptomatic improvement
2) ________ and _________ → interfere with hormone production
3) ________ and _________ → glandular destruction
1) B-blockers, corticosteroids → modify tissue response, symptomatic improvement
2) Thioamides, iodides → interfere with hormone production
3) Surgery, radioactive iodine → glandular destruction
Treatment of Myxedema Coma (end state of untreated hypothyroidism)
1) Large IV loading dose T4 + daily IV dosing
2) Hydrocortisone to prevent adrenal crisis as T4 increase may increase endogenous hydrocortisone metabolism
Treatment of thyroid storm:
4 meds and why?
Beta-Blockers: Propranolol → control CV symptoms
Sodium iodide IV + Potassium iodide → slow RELEASE of hormones
PTU → block hormone synthesis and T4 → T3 conversion
Hydrocortisone → block T4 to T3 conversion
Thyroidectomy
rarely used due to effective radioactive treatment
Advantage: rapid, permanent cure of hyperthyroidism
Diabetes and mood:
depression
bipolar disorders
Depression: 2-3x general population, worsens control of blood sugar
Bipolar Disorders: increased risk of also having DM2
- Higher rate of obesity for pts with bipolar
- Treatments for bipolar disorder → metabolic effects, weight gain
- Sleep apnea worsens insulin resistance
Hypercortisolemia and psych symptoms (6)
Psych symptoms may predate physical:
Depressive symptoms Anxiety Hypomanic/manic symptoms Psychosis Memory problems and other cognitive symptoms
what can occur in both hypo and hypercalcemia?
PSYCHOSIS**
Hyperparathyroidism with hypercalcemia:
pscyh symptoms?
Common: irritability, low mood, apathy, lethargy
Severe: delirium, psychosis, catatonia, coma
Hypocalcemia
psych symptoms
Common: anxiety, paresthesias, irritability
Severe: psychosis, manic symptoms, tetany, seizures
Addison’s disease
and psych symptoms
primary adrenal insufficiency
Psych symptoms: apathy, anhedonia, fatigue, depression
Acromegaly and psych symptoms
increased growth hormone
Psychiatric symptoms: irritability, mood lability, depressive symptoms, personality changes
Thyroid problems and psych symptoms interact how?
Thyroid hormone interacts with NE, serotonin, dopamine
Thyroid hormones appear to be capable of modulating phenotypic expression of illness
Hypothyroidism and psych symptoms
depression*, lethargy, forgetfulness (can be confused with dementia especially in older women), psychosis (later stages)
**Can have subclinical hypothyroidism unresponsive to antidepressants, and thyroid replacement may improve outcomes
Hyperthyroidism and psych symptoms
anxiety disorder, depressive disorder, mania when thyrotoxic
In Worrisome Growth you are worried about children having abnormal __________ or __________
height or growth velocity
What is considered worrisome growth for height?
short stature, height below 2 SD (3%) for age and gender OR height more than 3.5 inches below the midparental target height
What is considered worrisome growth for growth velocity
abnormally slow linear growth velocity or dropping across two major centile lines on the growth chart
Midparental target
97% of children fall within 3.5 inches of target
Boys → (Mom height + 5 inches + Dad height) / 2
Girls → (Dad height - 5 inches + Mom height) / 2
Skeletal maturation
direct correlation between degree of skeletal maturation and time of epiphyseal closure
Greater bone age delay = longer time before epiphyseal fusion ceases growth
Can be used to predict height by using child’s height and bone age BUT predictions NOT accurate in children with growth disorders
Normal variant of short stature (2)
1) Familial short stature
2) Constitutional growth delay
Familial short stature
children who have normal growth velocity and height that are within normal limits for parents’ heights
Initially will have decrease in growth rate between 6 and 18 months of age –> then track growth chart, but just lower than other people because their parents are short
Constitutional growth delay
aka “late bloomers”
born at normal weight/length with growth deceleration during first 2 years of life –> followed by normal growth paralleling lower percentile curve throughout prepubertal years
Should NOT be falling off after age 2-3 yrs
Skeletal maturation delayed**
Catch-up growth achieved by late puberty and delayed fusion of growth plates
Usually end up at lower end of normal height range for families
Treatment of Constitutional growth delay
Boys: testosterone if bone age > 11.5 yrs
Girls: estrogen
Failure to thrive
infants and toddlers < 2 years of age with:
Deceleration of weight gain < 3% or fall in weight across 2 or more major percentiles
-Typically primary weight issue with later height drop off
Non-organic causes most common (poor nutrition, psychosocial factors)
May look like constitutional growth delay
Nutritional growth retardation
linear growth stunting from poor weight gain in children > 2 yrs of age
May be secondary to systemic illnesses (celiac, IBD, CF), or stimulant medications
Hard to distinguish from constitutional growth delay/thinness
Weight typically falls off before height
Hypothyroidism and worrisome growth
profound growth failure, lacks common sx of hypothyroid seen in adults
Growth chart patterns: can have profound drop off on height + weight drop off
Cushing’s and worrisome growth
excessive weight gain, with falling off on height
small for gestational age
< 2SD for birth weight or length
Most healthy infants with SGH achieve catch-up in height by 2yr
Typically grow along a stable trajectory, but have height projection less than their genetic target
May have early or rapid puberty (compromises height)
**No delayed bone age - INTRINSIC short stature
Treatment for small for gestational age (SGA)
growth hormone treatment for kids who fail to have catch-up growth by age 2 years
Pathological causes of short stature
Nutritional (zinc, iron, anorexia, IBD, celiac disease, CF)
Endocrine:
1) Hypothyroid
2) Growth hormone deficiency
3) Cushing
4) Rickets
* *Two or more endocrine deficiency = BRAIN TUMOR until proven otherwise
Chromosomal:
1) Turner syndrome
2) Down syndrome
3) Prader-Willi Syndrome: GH deficient
4) Noonan syndrome
Others: skeletal dysplasias, metabolic, chronic diseases, psychosocial deprivation, drugs (stimulants, glucocorticoids)
Growth hormone deficiency
congenital and acquired causes
Congenital causes: Hypothalamic-pituitary malformations
1) Holoprosencephaly/Schizencephaly
2) Isolated cleft lip or palate
3) Septo-optic-dysplasia
4) Optic nerve hypoplasia
5) Empty sella syndrome
Acquired: trauma, CNS infection, hypophysitis, CNS tumors (craniopharyngioma, germinoma), cranial irradiation
Growth hormone deficiency
presentation
1) abnormal growth velocity with exclusion of other causes
2) Decreased muscle build
3) Increased subcutaneous fat (truncal)
4) Face immature for age
5) Prominent forehead, depressed midface
6) Small phallus (males)
7) Other midline facial defects
8) Prolonged jaundice +/- hypoglycemia in newborn period
Evaluation of growth hormone deficiency for worrisome growth (4)
1) Bone age
2) IGF-1
May be reduced due to malnutrition regardless of GH status
Can test IGFBP-3 instead - less affected by nutrition
3) Stimulation testing - clonidine, arginine, glucagon, L-dopa
4) MRI to evaluate for brain tumor, empty sella, etc. - high suspicion with other hormone deficiencies for tumor
Turner Syndrome (45X)
Haploinsufficiency of SHOX genes → Skeletal and growth abnormalities
Most common sex chromosome abnormality of females (1/2000)
No bone age delay (intrinsic short stature)
Will end up short, even with treatment with GH - no potential to reach height normal for their family
Not due to GH deficiency, due to SHOX gene deficiency
Presentation of turner syndrome
1) Short stature
2) Increased carrying angle
3) Short neck
4) Micro or retrognathia
5) Lymphatic obstruction (lymphedema)
6) Low hairline
7) Webbed neck
8) Cardiac abnormalities (bicuspid aortic valve, coarctation or aorta)
9) Renal - horseshoe kidney
10) Ovarian insufficiency
11) Hypothyroidism / celiac disease
Otitis media, hearing loss
12) Nonverbal learning disability
Short stature in Turner Syndrome
(final height 20 cm < target height if untreated)
Significant initial drop off on turner syndrome initially, and then have a secondary fall off around 5-6yrs, but if they have tall parents can be around 10-12yrs (can go unnoticed)
Treatment of growth in Turner Syndrome
growth hormone therapy (significantly improves growth and final adult height)
Start treatment as early as possible
8 tests you can do when evaluating worrisome growth
1) Bone age (left hand and wrist) → determine growth potential
2) Metabolic panel → rule out RTA, rickets
3) CBC → rule out anemia, chronic disease, skeletal dysplasia
4) TSH and T4
5) IGF-1 or IGFBP-3
6) Karyotype in girls → rule out Turner
7) TTG and IgA → rule out Celiac
8) ESR → rule out IBD
“FDA-approved” uses of growth hormone (9)
1985 - GH deficiency 1993 - chronic renal insufficiency 1996 - Adult growth hormone deficiency 1997 - Turner Syndrome 2000 - Prader-Willi Syndrome 2001 - small for gestational age (< 2 SDs) 2003 - idiopathic short stature 2006 - SHOX deficiency 2007 - Noonan syndrome
Side effects of GH treatment
slipped capital femoral epiphysis (hip or knee pain), intracranial hypertension (pseudotumor cerebri), insulin resistance
Determining a Good Clinical Practice Guideline:
8 steps/points of assessment
1) Transparency
2) Management of conflict of interests
3) Guideline group composition
4) Collaboration and coordination between systemic review and guideline development
5) Evidence foundation for recommendation
Judge certainty of net benefit based on evidence
6) Articulation of recommendation
7) External review
8) Update
____________ should be the first thing to look for when you are looking for how to treat a patient
Evidence based practice guideline
What is the best research evidence?
systematic reviews of RCTs
Systematic reviews
summary of best available evidence to address a focused question
Standard methods designed to reduce bias in systematic reviews
1) Focused question
2) Sources/search explicit, comprehensive
3) Selection is criterion based
4) Appraisal is critical
5) Synthesis is systematic
6) Inferences are evidence based
How do you critically appraise something?
3 questions to ask
Are results valid
Are valid results meaningful
Are the valid, meaningful results relevant to my patient
What kind of error can you have in a systematic review?
systematic error (bias) that causes results to be consistently distorted in one direction because of nonrandom factors
Two main types of bias in systematic reviews:
1) Publication bias
2) Location bias
Publication bias
tendency for published studies to differ systematically in their results from unpublished studies → significant studies more likely to be published
Location bias
tendency for high profile, widely disseminated studies to differ systematically in their results from low profile, less widely disseminated studies
Significant studies are easier to find
How to reduce publication and location bias? (4)
Avoid language restrictions
Search more than one electronic database
Search other types of documents
Check references of other studies
Contact experts or organizations
Meta-analysis is a ________ synthesis of data
Meta-analysis: QUANTITATIVE synthesis of data
Meta-analysis
STATISTICAL method for combining effect estimates of multiple studies to produce a single common estimate of effect
Improves precision by combining all available data
May or may NOT be part of a systematic review
Studies must have same outcome and be measured in similar ways
Disadvantages of meta-analysis
Does not control for bias
May inappropriately combine heterogeneous studies (adding apples to apples)
Problems in interpretation
Narrative review articles
structured summary and discussion of individual study characteristics and effect estimates
ALL relevant results should be presented
Use structured approach to presentation
How to deal with statistical heterogeneity: (4 strategies)
1) Do not pool at all
2) Ignore heterogeneity (use fixed effect model)
3) Allow for heterogeneity (use random effects model)
4) Explore heterogeneity through special statistical methods
